The config.json is a really simple JSON file.
which in most cases would look like this:

{
"port":80
}

The domains folder is the folder where all the magic happens.
Each folder inside that folder should represent the dns of the app in it.
So in the example above I host the websites proxy.example.com and example.com.
In each domain folder should be an main.js, which will be executed when your domain is initialized.